Dear Moderator,

PVElite evaluates stress ratio for each compoent while calculating hydrotest pressure.

I have a vessel with manhole. Manhole is with blind, here in nozzle dialogue there is no provision for selecting bolt material.

Hence PVElite is not considering bolt stress ratio while computing hydrotest pressure and that results in higher test pressure.

Kindly sort out the issue as it has a high impact whaen deciding hydrotest pressure based on MAWP.

Hello Purav

In the case of your manway, you probably did not do a separate calculation for the flange and blind cover (I am assuming this). However, in PV Elite you can do a calculation for the flange and cover, but you have to do this by adding a body flange to the model. It may look a little odd in the 3D model, but it will perform the calculation without a problem.

I have discussed the issue of bolt stress in another thread on the forum. When you initially assemble the flange and its mating cover (or other flange), you torque the bolts up to get a proper squeeze on the gasket. When you start to pressurise the system, the bolts stress does no really increase - it remains essentially the same. What happens is that the pressure on the gasket decreases.

At the hydrotest, the bolt stress is still about the same, but the pressure on the gasket decreases still further. So, the only thing you need worry about with the hydrotest, is that you do not get leakage.

Another this that may be surprising to you, is that as the design phase, you use PV Elite which gives a bolt allowable stress of around 25 000 psi (172 MPa). But, when the flanges are assembled, the fitter must get the stress up to at least 50 000 psi (344 MPa). That is about the only way of preventing leakage. I learned this when I attended a flange seminar in New Orleans one year.

Don't worry too much about the bolt stress. SA 193 B7 material is almost unbreakable. It is a very fancy high strength steel.

Hello Ray,

My question is very simple.

I want stress ratio of bolts to be considered while computing hydrotest pressure.

Here, our suggestion is to add (ask) bolt material whenever blind is checked in nozzle dialogue box.

Purav,

There is an interpretation from ASME which indicates that you do not have to consider the bolt stress ratio for the standard flanges, but only for the appendix 2 flanges.

Here is that interpretation,

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Interpretation: VIII-1-89-287
Subject: Section VIII, Division 1 (1986 Edition, 1988 Addenda), UG-99(b)
Date Issued: March 14, 1991
File: BC89-319

Question: Under the provisions of UG-99(b), may the ratio (S test temperatures design temperature) for the bolting material be used in calculating the required hydrostatic test pressure if it results in the lowest ratio for the material of which the vessel is constructed for:

(1) bolted flange connections designed per Appendix 2?
(2) bolted flange connection which comply with an ANSI product standard or a Manufacturer's standard as permitted in UG-11?

Reply:
(1) Yes.
(2) No; the limiting hydrostatic test pressure shall be established in accordance with the applicable standard

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So, the real question is what kind of flange do you have attached on the end of the flange. If it is a custom flange, then Ray's post above is appropriate. Other wise for standard flanges the above interpretation provides guidance to ignore the bolt stress ratio.

Dear Ray/Mandeep,

We have also referred to follwing ASME interepretation;

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Interpretation: VIII-1-83-128
Subject: Section VIII, Divisions 1 and 2, UG-99 and AT-300, Consideration of Bolting Material
Date Issued: April 28, 1983
File: BC83-072

Question (1): In establishing hydrostatic test pressures in accordance with UG-99 of Division 1 and Article T-3 of Division 2, shall the allowable stress of bolts be considered?

Reply (1): Yes.

========================================================

Kindly check & revert.

Purav,

There is a distinction between the bolts on the "standard" flange v/s bolts on a custom flange.

Mandeep ,
Can u please elaborate the difference between bolts on the "standard" flange v/s bolts on a custom flange.?


I understand Interpretation: VIII-1-83-128 is applicable for bolts on any flange.

As per Interpretation: VIII-1-89-287,the limiting hydrostatic test pressure shall be established in accordance with the applicable standard...can u please clarify which standard???

Sure ARG,

The clue is in the interpretation that I referenced, VIII-1-89-287

There are 2 types of flanges quoted in this interpretation, the 1st one is the custom flane, meaning that you would perform an ASME Appendix 2 analysis to check the flange.

The 2nd one is a standard flange, such as B16.5 or B16.47, where you select the flange based on class, grade and get pressure rating from a table.

Per this interpretation, the answer is to consider the bolt stress ratio for a custom flange and not for a standard flange

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(1) bolted flange connections designed per Appendix 2?
(2) bolted flange connection which comply with an ANSI product standard or a Manufacturer's standard as permitted in UG-11?

Reply:
(1) Yes.
(2) No; the limiting hydrostatic test pressure shall be established in accordance with the applicable standard

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